Adelophthalmidae
   HOME

TheInfoList



OR:

Adelophthalmidae (the name deriving from the
type genus In biological taxonomy, the type genus (''genus typica'') is the genus which defines a biological family and the root of the family name. Zoological nomenclature According to the International Code of Zoological Nomenclature, "The name-bearin ...
''
Adelophthalmus ''Adelophthalmus'' is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of ''Adelophthalmus'' have been discovered in deposits ranging in age from the Early Devonian to the Early Permian, which makes it the longest lived of ...
'', meaning "no obvious
eyes An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...
") is a
family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
of
eurypterid Eurypterids, often informally called sea scorpions, are a group of extinct marine arthropods that form the Order (biology), order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period, 467.3 Myr, mil ...
s, an
extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
group of aquatic
arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...
s. Adelophthalmidae is the only family classified as part of the superfamily Adelophthalmoidea, which in turn is classified within the
infraorder Order () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between Family_(biology), family and Class_(biology), class. In biological classification, the order is a taxonomic rank used in the classific ...
Diploperculata Diploperculata is an infraorder of eurypterids, an extinct group of aquatic arthropods commonly known as "sea scorpions". The name, derived from Greek διπλόω ("double") and ''operculum'', refers to the distinguishing feature that unites the ...
in the
suborder Order () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and recognized ...
Eurypterina Eurypterina is one of two suborders of eurypterids, an extinct group of chelicerate arthropods commonly known as "sea scorpions". Eurypterine eurypterids are sometimes informally known as "swimming eurypterids". They are known from fossil depos ...
. Adelophthalmid eurypterids were small and
swimming Swimming is the self-propulsion of a person through water, such as saltwater or freshwater environments, usually for recreation, sport, exercise, or survival. Swimmers achieve locomotion by coordinating limb and body movements to achieve hydrody ...
eurypterids that appeared in the
Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...
period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...
. With the earliest known members of the group, '' Nanahughmilleria prominens'' and '' Parahughmilleria maria'', being known from deposits of Early Silurian (possibly the
Llandovery Llandovery (; ) is a market town and community (Wales), community in Carmarthenshire, Wales. It lies on the River Tywi and at the junction of the A40 road, A40 and A483 road, A483 roads, about north-east of Carmarthen, north of Swansea and w ...
epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided b ...
) age and the last members, belonging to the long-lasting and widespread
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
''Adelophthalmus'', going extinct in the
Early Permian 01 or 01 may refer to: * The year 2001, or any year ending with 01 * The month of January * 1 (number) Music * '01 (Richard Müller album), ''01'' (Richard Müller album), 2001 * 01 (Urban Zakapa album), ''01'' (Urban Zakapa album), 2011 * ''01011 ...
, the Adelophthalmidae is the longest lasting single family of eurypterids. The survival of the group, and of swimming eurypterids (the suborder Eurypterina) beyond the Late
Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
is entirely due to the survival, and subsequent success, of ''Adelophthalmus'' throughout the Devonian and
Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...
. ''Adelophthalmus'' (and possibly '' Unionopterus'') represents the only known genus of swimming eurypterids beyond the extinction of the rest of the group in the Late Devonian, extending the temporal range of the group by over a hundred million years. Though the last swimming eurypterids and the final members of the traditionally more successful and numerous suborder Eurypterina, the adelophthalmids were not the last eurypterids. The
stylonurine Stylonurina is one of two suborders of eurypterids, a group of extinct arthropods commonly known as "sea scorpions". Members of the suborder are collectively and informally known as "stylonurine eurypterids" or "stylonurines". They are known from ...
s or the "walking eurypterids" were the last ones, surviving in the family
Hibbertopteridae Hibbertopteridae (the name deriving from the type genus ''Hibbertopterus'', meaning "Hibbert's wing") is a family of eurypterids, an extinct group of aquatic arthropods. They were members of the superfamily Mycteropoidea. Hibbertopterids were lar ...
until the
Permian–Triassic extinction event The Permian–Triassic extinction event (also known as the P–T extinction event, the Late Permian extinction event, the Latest Permian extinction event, the End-Permian extinction event, and colloquially as the Great Dying,) was an extinction ...
or shortly before a few million years after the extinction of the adelophthalmids in the Early Permian.


Description

The size of the adelophthalmid
eurypterid Eurypterids, often informally called sea scorpions, are a group of extinct marine arthropods that form the Order (biology), order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period, 467.3 Myr, mil ...
s ranged from 4 centimetres (1.6 inch) to 32 cm (12.6 in), the smallest
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
being '' Nanahughmilleria clarkei'' and the largest one being '' Adelophthalmus khakassicus''. The adelophthalmids were relatively small compared to their relatives, such as the gigantic
pterygotid Pterygotidae (the name deriving from the type genus ''Pterygotus'', meaning "winged one") is a family of eurypterids, an extinct group of aquatic arthropods. They were members of the superfamily Pterygotioidea. Pterygotids were the largest known ...
''
Jaekelopterus rhenaniae ''Jaekelopterus'' is a genus of predatory eurypterid, a group of extinct aquatic arthropods. Fossils of ''Jaekelopterus'' have been discovered in deposits of Early Devonian age, from the Pragian and Emsian stages. There are two known species: t ...
'', which easily exceeded 2 metres (6.5 feet), and was the largest
arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...
ever discovered. The adelophthalmids were small swimming eurypterids with a parabolic (approximately U-shaped)
carapace A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the unde ...
(the
dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage The fus ...
plate of the head, '' Unionopterus'' possibly representing an exception) and with intramarginal (occurring within the margin)
eyes An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...
. The swimming leg (sixth
limb Limb may refer to: Science and technology *Limb (anatomy), an appendage of a human or animal *Limb, a large or main branch of a tree *Limb, in astronomy, the curved edge of the apparent disk of a celestial body, e.g. lunar limb *Limb, in botany, t ...
) was of ''Adelophthalmus''-type, that is, with a seventh
podomere The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments (called podomeres) are of Latin origin, and may be confused with terms for bones: ''coxa'' (meaning hip, : ...
(segments of the limbs) long and an eighth podomere coarsely serrated. The body had a midsection second order differentiation present (that is, with lateral "extensions" in the seventh body segment) and with a lanceolate (lance-shaped)
telson The telson () is the hindmost division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment (biology), segment of the arthropod body, or an additional division that is not a true segm ...
(the posteriormost division of the body). The
morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...
of the group varies depending on how derived (evolutionary advanced) the
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
was. In fact, from the basal ("primitive") ''Nanahughmilleria'' to the more derived ''Adelophthalmus'', a gradual decrease in the spinosity (possessing spines) of the
appendages An appendage (or outgrowth) is an external body part or natural prolongation that protrudes from an organism's body such as an arm or a leg. Protrusions from single-celled bacteria and archaea are known as cell-surface appendages or surface app ...
(limbs) and an increase in the size of the genital spatulae (a long, flat piece in the genital area) occurred. The even more primitive '' Pittsfordipterus'' probably did not even possess the latter.


History of research

The first adelophthalmid
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...
s to be uncovered were those of the
type genus In biological taxonomy, the type genus (''genus typica'') is the genus which defines a biological family and the root of the family name. Zoological nomenclature According to the International Code of Zoological Nomenclature, "The name-bearin ...
, ''Adelophthalmus''. The German
paleontologist Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...
Hermann Jordan collected the first specimen of the species ''A. granosus'' at Jägersfreude in
Saarland Saarland (, ; ) is a state of Germany in the southwest of the country. With an area of and population of 990,509 in 2018, it is the smallest German state in area apart from the city-states of Berlin, Bremen, and Hamburg, and the smallest in ...
,
Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...
. The specimen would be described three years later by Jordan and
Hermann von Meyer Christian Erich Hermann von Meyer (3 September 1801 – 2 April 1869), known as Hermann von Meyer, was a German palaeontologist. He was awarded the 1858 Wollaston medal by the Geological Society of London. Life He was born in Frankfurt am ...
, who immediately recognized the eurypterid nature of the fossils by the great resemblance of the overall shape and form of the carapace and appendages with that of ''
Eurypterus ''Eurypterus'' ( ) is an extinct genus of eurypterid, a group of organisms commonly called "sea scorpions". The genus lived during the Silurian period, from around 432 to 418 million years ago. ''Eurypterus'' is by far the most well-studied and ...
''. One of the main differences that Jordan and von Meyer noticed was the apparent lack of eyes, which gives name to ''Adelophthalmus'' (meaning "no obvious eyes") and the entire superfamily. This feature is now assumed to be due to a preservational artifact and that was not present in ''Adelophthalmus'', nor in any other adelophthalmid. Since then, a total of 33 species have been described, some of which have been historically classified within other genera (''Anthraconectes'', ''Glyptoscorpius'', ''Lepidoderma'' and ''Polyzosternites'', all now synonymous with ''Adelophthalmus''), making ''Adelophthalmus'' the most
diverse Diversity, diversify, or diverse may refer to: Business *Diversity (business), the inclusion of people of different identities (ethnicity, gender, age) in the workforce * Diversity marketing, marketing communication targeting diverse customers ...
eurypterid genus to date. However, many of these species are fragmentary and could represent synonyms of other species within ''Adelophthalmus'' or even species of other genera. It is possible that the large amount of species in ''Adelophthalmus'' will eventually provoke its separation into two or three separate genera. In 1948, the Ukrainian paleontologist and
geologist A geologist is a scientist who studies the structure, composition, and History of Earth, history of Earth. Geologists incorporate techniques from physics, chemistry, biology, mathematics, and geography to perform research in the Field research, ...
Boris Isidorovich Chernyshev described a new genus known by one single specimen from
Kazakhstan Kazakhstan, officially the Republic of Kazakhstan, is a landlocked country primarily in Central Asia, with a European Kazakhstan, small portion in Eastern Europe. It borders Russia to the Kazakhstan–Russia border, north and west, China to th ...
(at that time part of the
Soviet Union The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...
) and tentatively classified it as part of the Pterygotidae
family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
. It was named ''Unionopterus'', and its
classification Classification is the activity of assigning objects to some pre-existing classes or categories. This is distinct from the task of establishing the classes themselves (for example through cluster analysis). Examples include diagnostic tests, identif ...
is controversial due to the poor illustrations given by Chernyshev and the fact that the only known fossil is presumed to be lost. The genus has been treated as an indeterminate eurypterid, an adelophthalmid or a member of the genus ''Adelophthalmus'', as well as completely ignored. The spinosity of its appendages may suggest the second option, but this is not entirely certain and the
phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...
classification of ''Unionopterus'' may never be resolved. In 1961, the American paleontologist Erik Norman Kjellesvig-Waering considered several species of the genus ''
Hughmilleria ''Hughmilleria'' is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of ''Hughmilleria'' have been discovered in deposits of the Silurian age in China and the United States. Classified as part of the basal family Hughmille ...
'' sufficiently different from the
type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
to be separated into a new
subgenus In biology, a subgenus ( subgenera) is a taxonomic rank directly below genus. In the International Code of Zoological Nomenclature, a subgeneric name can be used independently or included in a species name, in parentheses, placed between the ge ...
, which he named ''Nanahughmilleria''. These species shared a key characteristic, small intramarginal eyes of reniform form (bean-shaped), in contrast to the large ovoid eyes placed in the margin of the carapace present in the genotype and its allied forms. Kjellesvig-Waering designated ''H.'' (''Nanahughmilleria'') ''norvegica'' as the type species of the new subgenus. At the same time, he erected a new genus, '' Parahughmilleria'', with ''P. salteri'' as the type species. Kjellesvig-Waering based its new
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
mainly on the presence of supplementary
lobe Lobe may refer to: People with the name * Lobe (surname) Science and healthcare * Lobe (anatomy) * Lobe, a large-scale structure of a radio galaxy * Glacial lobe, a lobe-shaped glacier * Lobation, a characteristic of the nucleus of certain biolo ...
s (
distal Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position provi ...
lobes in a plate-like segment which contains the genital aperture called genital operculum), as well as in the intramarginal eyes. In 1964, Kjellesvig-Waering described the genital operculum of the species ''H.'' (''N.'') ''phelpsae'' and suggested that this part of the body could have great phylogenetic importance in the future. Two years later, together with the American paleontologist Kenneth Edward Caster, he raised ''H.'' (''N.'') ''phelpsae'' to the generic level under the name ''Pittsfordipterus''. They also described a new genus and species, '' Bassipterus virginicus''. It differs essentially from other adelophthalmids by the specialization of its genital appendage, with characteristics reminiscent of ''Eurypterus''. In 1989, Victor P. Tollerton Jr. described the family Adelophthalmidae along with many others, including ''Adelophthalmus'', ''Parahughmilleria'', ''Bassipterus'' and ''Unionopterus''. This clade was based on the presence of spines in the second to fifth pair of appendages, a swimming leg of ''Adelophthalmus''-type and the presence of epimera (lateral "extensions" of the segment) in the seventh segment. Tollerton commented that some species of ''Adelophthalmus'' that did not have spines in the appendages may be better placed in a new genus in the family
Slimonidae Slimonidae (the name deriving from the type genus ''Slimonia'', which is named in honor of Welsh fossil collector and surgeon Robert Slimon) is a family of eurypterids, an extinct group of aquatic arthropods. Slimonids were members of the super ...
(he mentioned the now invalid Slimonioidea). Although a new genus for spineless species could be phylogenetically supported, moving it to Slimonidae based on the loss of a feature which seems to have been lost separately in the two groups is not in line with common practice. Odd Erik Tetlie in an unpublished
thesis A thesis (: theses), or dissertation (abbreviated diss.), is a document submitted in support of candidature for an academic degree or professional qualification presenting the author's research and findings.International Standard ISO 7144: D ...
of 2004 erected the superfamily Adelophthalmoidea and the family Nanahughmilleridae. Adelophthalmoidea was diagnosed as eurypterids with parabolic carapaces, small reniform eyes, appendages of variable spinosity and a lanceolate telson, among others. This superfamily would be formally described two years later by Tetlie and Peter Van Roy. On the other hand, Nanahughmilleridae was described to contain the adelophthalmoids with no or reduced genital spatulae and the second to fifth pair of
prosoma The cephalothorax, also called prosoma in some groups, is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. (The terms ''prosoma'' and ''opisthosoma'' are equivalent to ''cepha ...
l (of the prosoma, "head") appendages of ''Hughmilleria''-type. This family contained ''Nanahughmileria'', ''Pittsfordipterus'' and perhaps ''Parahughmilleria''. However, the clade has almost never been used in subsequent studies and lists of eurypterids, and instead, they classify the nanahughmillerids as part of Adelophthalmidae. In 2008, ''Nanahughmilleria patteni'' was recognized as a different and much more basal species, and therefore a new genus, '' Eysyslopterus'', was named by Tetlie and Markus Poschmann. The carapace of ''Eysyslopterus'' and other basal members of the closely related
Pterygotioidea Pterygotioidea (the name deriving from the type genus ''Pterygotus'', meaning "winged one") is a superfamily (taxonomy), superfamily of eurypterids, an extinct group of aquatic arthropods. Pterygotioids were the most Derived trait, derived membe ...
('' Herefordopterus'') and the waeringopteroids (''
Orcanopterus ''Orcanopterus'' is a genus of a eurypterid classified as part of the family Waeringopteridae. The genus contains one species, ''O. manitoulinensis'', from the Ordovician of Manitoulin District, Manitoulin, Canada. Morphology Limbs ''Orca ...
'') has been shown as almost identical, only differing between them by the position of the eyes. Due to the intramarginal position of the eyes, ''Eysyslopterus'' has been classified within Adelophthalmidae, but it has also been suggested that it is the
sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...
(closest relative) of a clade formed by Adelophthalmoidea and Pterygotioidea. However, this can not be demonstrated until more fossil material is found. In 2023, '' Archopterus anjiensis'', a new genus and species, was described based on a single specimen found in the
Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...
-aged Wenchang Formation of
Zhejiang ) , translit_lang1_type2 = , translit_lang1_info2 = ( Hangzhounese) ( Ningbonese) (Wenzhounese) , image_skyline = 玉甑峰全貌 - panoramio.jpg , image_caption = View of the Yandang Mountains , image_map = Zhejiang i ...
,
China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
, representing the oldest known record of the Adelophthalmidae, extending the stratigraphic record of the family some 10 million years older from the early
Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...
into the late Ordovician.


Evolutionary history

The eurypterids as a group peaked in diversity during the Silurian, of the approximately 250 valid species accounted for as of , around 139 (≈56 %) were from the Silurian alone. Many eurypterid groups are first recorded from the Silurian, such as Pterygotioidea,
Mycteropoidea Mycteropoidea is an extinct superfamily of eurypterids, an extinct group of chelicerate arthropods commonly known as "sea scorpions". It is one of four superfamilies classified as part of the suborder Stylonurina. Mycteropoids have been recovered ...
,
Stylonuroidea Stylonuroidea is an extinct superfamily of eurypterids, an extinct group of chelicerate arthropods commonly known as "sea scorpions". It is one of four superfamilies classified as part of the suborder Stylonurina. Stylonuroidea, which lived from ...
and Adelophthalmoidea itself. The most primitive members of Adelophthalmoidea evolved in
Laurussia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around (Million years ago, Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during ...
(an ancient
supercontinent In geology, a supercontinent is the assembly of most or all of Earth's continent, continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", ...
, also known as Euramerica). In fact, the most basal species of the clade so far (''Eysyslopterus patteni'') has been recovered from
Ludlovian The Ludlow Group are geologic formations deposited during the Ludlow epoch of the Silurian period in the British Isles, in areas of England, Ireland, Scotland, and Wales. Formations This group contains the following formations in descending or ...
(around 427–423 mya) deposits of the
paleocontinent A paleocontinent or palaeocontinent is a distinct area of continental crust that existed as a major landmass in the geological past. There have been many different landmasses throughout Earth's time. They range in sizes; some are just a collection ...
Baltica Baltica is a paleocontinent that formed in the Paleoproterozoic and now constitutes northwestern Eurasia, or Europe north of the Trans-European Suture Zone and west of the Ural Mountains. The thick core of Baltica, the East European Craton, i ...
(
Scandinavia Scandinavia is a subregion#Europe, subregion of northern Europe, with strong historical, cultural, and linguistic ties between its constituent peoples. ''Scandinavia'' most commonly refers to Denmark, Norway, and Sweden. It can sometimes also ...
and
Eastern Europe Eastern Europe is a subregion of the Europe, European continent. As a largely ambiguous term, it has a wide range of geopolitical, geographical, ethnic, cultural and socio-economic connotations. Its eastern boundary is marked by the Ural Mountain ...
, precisely
Estonia Estonia, officially the Republic of Estonia, is a country in Northern Europe. It is bordered to the north by the Gulf of Finland across from Finland, to the west by the Baltic Sea across from Sweden, to the south by Latvia, and to the east by Ru ...
). However, it is not possible to determine where the clade originated, probably in Baltica or
Laurentia Laurentia or the North American craton is a large continental craton that forms the Geology of North America, ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of ...
(most of eastern continental
North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
). Although most of the representatives of Adelophthalmoidea have been found in Laurentia,
Avalonia Avalonia was a microcontinent in the Paleozoic era. Crustal fragments of this former microcontinent are terranes in parts of the eastern coast of North America: Atlantic Canada, and parts of the East Coast of the United States, East Coast of the ...
(Germany,
Great Britain Great Britain is an island in the North Atlantic Ocean off the north-west coast of continental Europe, consisting of the countries England, Scotland, and Wales. With an area of , it is the largest of the British Isles, the List of European ...
, parts of eastern North America) and Baltica (that is, Laurussia), the nearly
cosmopolitan Cosmopolitan may refer to: Internationalism * World citizen, one who eschews traditional geopolitical divisions derived from national citizenship * Cosmopolitanism, the idea that all of humanity belongs to a single moral community * Cosmopolitan ...
(worldwide) genus ''Adelophthalmus'' was also present in the Rheno-Hercynian Terrane (western and central Europe),
Siberia Siberia ( ; , ) is an extensive geographical region comprising all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has formed a part of the sovereign territory of Russia and its predecessor states ...
and in the
Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...
part of the current
Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
. In the Silurian, most of the adelophthalmid genera would appear, but all went extinct soon after or in the
Middle Devonian In the geological timescale, the Middle Devonian epoch (from 393.3 ± 1.2 million years ago to 382.7 ± 1.6 million years ago) occurred during the Devonian period, after the end of the Emsian age. The Middle Devonian epoch is subdivided into two ...
. The oldest representatives of the group were ''Parahughmilleria maria'' and ''Nanahughmilleria prominens'', both from the
Llandovery Llandovery (; ) is a market town and community (Wales), community in Carmarthenshire, Wales. It lies on the River Tywi and at the junction of the A40 road, A40 and A483 road, A483 roads, about north-east of Carmarthen, north of Swansea and w ...
(around 444–433 mya), suggesting that the adelophthalmids first appeared around this
epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided b ...
. This is supported by the appearance of the basal pterygotioids, the sister group of the adelophthalmoids, in the Llandovery. However, the fossil record of Adelophthalmoidea is very poor in the Early Silurian and both species have disputed ages. The unequivocally oldest representative was ''P. hefteri'', with fossils found in the Kip Burn Formation,
Lesmahagow Lesmahagow ( ; or ''Lesmahagae'', ) is a small town in the historic county of Lanarkshire on the edge of moorland, near Lanark in the central belt of Scotland. Lesmahagow was also a civil parish. It lies west of the M74 motorway, M74, and sout ...
,
Scotland Scotland is a Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the United Kingdom's land area, consisting of the northern part of the island of Great Britain and more than 790 adjac ...
, from the beginning of the
Wenlockian The Wenlock Epoch (sometimes referred to as the Wenlockian) is the second epoch of the Silurian. It is preceded by the Llandovery Epoch and followed by the Ludlow Epoch. Radiometric dates constrain the Wenlockian between and million years ago. ...
epoch (around 433–427 mya). These fossils differ slightly in the proportions of the body with the fossils of its type locality (in Germany) and have been compared with the latter ones, but the assignment of the Scottish fossils to ''P. hefteri'' is not entirely certain. The first species lived in
brackish Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...
-
estuarine An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...
water or in fully
marine habitats A marine habitat is a habitat that supports marine life. Marine life depends in some way on the saltwater that is in the sea (the term ''marine'' comes from the Latin ''mare'', meaning sea or ocean). A habitat is an ecological or environmen ...
. In the
Emsian The Emsian is one of three faunal stages in the Early Devonian Epoch. It lasted from 410.62 ±1.95 million years ago to 393.47 ±0.99 million years ago. It was preceded by the Pragian Stage and followed by the Eifelian Stage. It is named after ...
(around 393–408 mya, in Early Devonian), the earliest species of ''Adelophthalmus'' appeared, ''A. sievertsi'', presenting basal features such as the wide swimming leg (as in ''Nanahughmilleria'' and ''Parahughmilleria''). The eurypterids were one of the groups most heavily affected by the
Late Devonian extinction event The Late Devonian mass extinction, also known as the Kellwasser event, was a mass extinction event which occurred around 372 million years ago, at the boundary between the Frasnian and Famennian ages of the Late Devonian period.Racki, 2005McGh ...
, following a major decline in diversity during the Early Devonian, eurypterids were rare in marine
environments Environment most often refers to: __NOTOC__ * Natural environment, referring respectively to all living and non-living things occurring naturally and the physical and biological factors along with their chemical interactions that affect an organism ...
by the
Late Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era during the Phanerozoic eon, spanning 60.3 million years from the end of the preceding Silurian period at million years ago ( Ma), to the beginning of the succeeding ...
. Of the 16 eurypterid families that had been alive at the beginning of the Devonian, only three persisted into the
Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...
, all of them non-marine groups. The
suborder Order () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and recognized ...
Eurypterina Eurypterina is one of two suborders of eurypterids, an extinct group of chelicerate arthropods commonly known as "sea scorpions". Eurypterine eurypterids are sometimes informally known as "swimming eurypterids". They are known from fossil depos ...
was rendered almost completely extinct, only surviving Adelophthalmoidea (represented by ''Adelophthalmus''). ''Adelophthalmus'' would rapidly diversify, already being present in Siberia and Gondwana (Australia) since the Devonian. In the Carboniferous, the distribution of ''Adelophthalmus'' became approximately circumequatorial (around the
Equator The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...
). Out of the 33 species referred to ''Adelophthalmus'', 23 (69%) were from the Carboniferous alone, reaching its peak diversity in the Late Carboniferous and becoming the most common of all eurypterids of the Late
Paleozoic The Paleozoic ( , , ; or Palaeozoic) Era is the first of three Era (geology), geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma a ...
. This quick diversification may be due to their morphology, converting the adelophthalmids in one of the most able swimmers among the eurypterids. The
amalgamation Amalgamation is the process of combining or uniting multiple entities into one form. Amalgamation, amalgam, and other derivatives may refer to: Mathematics and science * Amalgam (chemistry), the combination of mercury with another metal **Pan ama ...
(union) of
Pangaea Pangaea or Pangea ( ) was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous period approximately 335 mi ...
into a global supercontinent was also an important factor. The pterygotoids were also successful swimmers, but they went extinct in the Middle Devonian, long before the formation of Pangea. Although ''Unionopterus'' also appeared in the Carboniferous, this genus is very little known and is usually ignored by the eurypterid researchers. During the Late Carboniferous and Early Permian, ''Adelophthalmus'' lived in brackish and
freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include non-salty mi ...
environments adjacent to
coastal plain A coastal plain (also coastal plains, coastal lowland, coastal lowlands) is an area of flat, low-lying land adjacent to a sea coast. A fall line commonly marks the border between a coastal plain and an upland area. Formation Coastal plains can f ...
s, a type of common and stable
habitat In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...
at the time. Although the formation of Pangea helped the genus to widespread, it also affected its environments. They began to disappear due to a
climatic change ''Climatic Change'' is a biweekly peer-reviewed scientific journal published by Springer Science+Business Media covering cross-disciplinary work on all aspects of climate change and variability. It was established in 1977 by Stephen H. Schneider, ...
that caused alterations of depositional and vegetational patterns across the world, provoking a decrease in number of the genus. ''A. sellardsi'' from the
Artinskian In the geologic timescale, the Artinskian is an age (geology), age or stage (stratigraphy), stage of the Permian. It is a subdivision of the Cisuralian Epoch (geology), Epoch or series (stratigraphy), Series. The Artinskian likely lasted between ...
(around 290–284 mya, Early Permian) epoch of
Kansas Kansas ( ) is a landlocked U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to the west. Kansas is named a ...
,
United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
, was the last species of ''Adelophthalmus'' and therefore of all the suborder Eurypterina. The genus expanded the temporal range of the suborder by about 100 million years and turned its family to the longest lasting single family of eurypterids. Nevertheless, the eurypterids continued to exist represented by the stylonurids. The Russian
hibbertopterid Hibbertopteridae (the name deriving from the type genus ''Hibbertopterus'', meaning "Samuel Hibbert-Ware, Hibbert's wing") is a family of Eurypterid, eurypterids, an extinct group of aquatic Arthropod, arthropods. They were members of the superfam ...
species '' Campylocephalus permianus'' persisted until the
Changhsingian In the geologic time scale, the Changhsingian or Changxingian is the latest age or uppermost stage of the Permian. It is also the upper or latest of two subdivisions of the Lopingian Epoch or Series. The Changhsingian lasted from to 251.9 Ma a ...
(around 254–252 mya, Late Permian) stage, being the last known eurypterid. No eurypterids are known from fossil beds higher than the Permian, indicating that they probably died out in the Permian–Triassic mass extinction event or shortly before.


Classification


External phylogeny

The adelophthamids are classified within the
infraorder Order () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between Family_(biology), family and Class_(biology), class. In biological classification, the order is a taxonomic rank used in the classific ...
Diploperculata Diploperculata is an infraorder of eurypterids, an extinct group of aquatic arthropods commonly known as "sea scorpions". The name, derived from Greek διπλόω ("double") and ''operculum'', refers to the distinguishing feature that unites the ...
, in the Eurypterina suborder of eurypterids. The infraorder Diploperculata contains the four most derived superfamilies of eurypterine eurypterids;
Carcinosomatoidea Carcinosomatoidea is an extinct superfamily of eurypterids, an extinct group of chelicerate arthropods commonly known as "sea scorpions". It is one of the superfamilies classified as part of the suborder Eurypterina. Some carcinosomatoid genera ...
, Adelophthalmoidea, Pterygotioidea and the waeringopteroids, united by the shared feature that the genital operculum (the structure that contains the genital appendage) is made up of two fused segments. Adelophthalmoidea was one of the most diverse taxonomically eurypterid clades, with about 40 species described. The sister group of Adelophthalmoidea, Pterygotioidea, surpassed this amount with around 50 described species, becoming the most diverse superfamily to date. These sister-clades are the most derived in the Eurypterina and make up more than a third of all the species of eurypterids, with almost 100 species between both of them. The
cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...
below is simplified from 2007 study by O. Erik Tetlie, showcasing the position of Adelophthalmoidea within the suborder Eurypterina. Placement of Diploperculata follows Lamsdell ''et al.'' 2013.


Internal phylogeny

All adelophthalmids have a series of shared characteristics that make them different from the rest of eurypterids. However, some genera developed different features within Adelophthalmidae that divide the family into several smaller clades and groupings. The genera ''Parahughmilleria'' and ''Adelophthalmus'' form a derived clade based on the presence of enlarged spines on at least one podomere in the appendage V (fifth limb), the presence of epimera in the postabdomen (body segments 8 to 12) and the large spatulae that has been associated with the genital operculum. ''Nanahughmilleria'' is placed as the sister taxon of this clade but more basal due to the increased spinosity of its appendage V and in the small size of the genital spatulae. ''Bassipterus'' and ''Pittsfordipterus'' are positioned as relatively more basal to this clade and form a group supported by two
synapomorphies In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to ...
(shared characteristics different from that of their
latest common ancestor A most recent common ancestor (MRCA), also known as a last common ancestor (LCA), is the most recent individual from which all organisms of a set are inferred to have descended. The most recent common ancestor of a higher taxon is generally assu ...
); long narrow eyes and a complex termination of the genital appendage. At the base of the family, ''Eysyslopterus'' has been interpreted as the most basal adelophthalmid. The carapace of this genus, ''Herefordopterus'' and ''Orcanopterus'' were almost identical and were mainly differentiated by the eye position. In the latter, the eyes were almost marginal, but were separated from margin by the marginal rim. The eyes of ''Herefordopterus'' were completely marginal, a characteristic present in all the pterygotioid genera. Although the eyes of ''Eysyslopterus'' were intramarginal, they were much closer to the margin than in its relatives, suggesting that the eyes gradually migrated towards the center of the carapace from the basal genera to the derived ''Adelophthalmus''. The position of its eyes has led some researchers to question whether ''Eysyslopterus'' is an adelophthalmid at all or a sister taxon of Adelophthalmidae, but more fossils are required to either prove or disprove its phylogenetic position within the family or outside it. The cladogram below presents the inferred phylogenetic positions of most of the genera included in the three most derived superfamilies of the Eurypterina suborder of eurypterids (Adelophthalmoidea, Pterygotioidea and the waeringopteroids), as inferred by O. Erik Tetlie and Markus Poschmann in 2008, based on the results of a 2008 analysis specifically pertaining to the Adelophthalmoidea and a preceding 2004 analysis.


Paleoecology

The adelophthalmids as a whole inhabited environments situated near the coastal realm, with preferences in
lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') an ...
s, estuaries or
deltas A river delta is a landform, wikt:archetype#Noun, archetypically triangular, created by the deposition (geology), deposition of the sediments that are carried by the waters of a river, where the river merges with a body of slow-moving water or ...
, which have reduced
salinity Salinity () is the saltiness or amount of salt (chemistry), salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensio ...
. A marine influence is commonly found in horizons (
sections Section, Sectioning, or Sectioned may refer to: Arts, entertainment and media * Section (music), a complete, but not independent, musical idea * Section (typography), a subdivision, especially of a chapter, in books and documents ** Section sig ...
of the fossil site) that comprise eurypterids, but marine index fossils (fossils that indicate a marine environment and ecosystem) in many cases are not associated with eurypterids. In some cases, where the adelophthalmids are very rare, the fossils could have been deposited in a different place from the one they originated, exemplified by ''A. waterstoni'', which is known from a single specimen that is in turn the only eurypterid of the zone, the
Gogo Formation The Gogo Formation in the Kimberley region of Western Australia is a Lagerstätte that exhibits exceptional preservation of a Devonian reef community. The formation is named after Gogo Station, a cattle station where outcrops appear and fossi ...
of Australia, where more than 2,000
crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...
s have been found. The first adelophthalmids, for example the Scottish ''Parahughmilleria hefteri'', have been conserved in non-marine brackish-estuarine habitats, with possible
tidal Tidal is the adjectival form of tide. Tidal may also refer to: * ''Tidal'' (album), a 1996 album by Fiona Apple * Tidal (king), a king involved in the Battle of the Vale of Siddim * TidalCycles, a live coding environment for music * Tidal (servic ...
influence, although basal forms that inhabited completely marine deposits are known. This preference remained constant in Adelophthalmidae until ''Adelophthalmus'' appeared. In deposits of the Early Devonian of Germany, where ''Parahughmilleria hefteri'' and ''Adelophthalmus sievertsi'' coexisted, a more obvious marine influence is observed in the sections dominated by ''Parahughmilleria'' than in those dominated by ''Adelophthalmus''. This suggests that ''Adelophthalmus'' had a preference for habitats dominated by freshwater, unlike other more basal forms. This preference for freshwater habitats is stronger during the
Bashkirian The Bashkirian is in the International Commission on Stratigraphy geologic timescale the lowest stage (stratigraphy), stage or oldest age (geology), age of the Pennsylvanian (geology), Pennsylvanian. The Bashkirian age lasted from to Mega annu ...
and
Moscovian Moscovian may refer to: *An inhabitant of Moscow, the capital of Russia *Something of, from, or related to Moscow *Moscovian (Carboniferous) The Moscovian is in the International Commission on Stratigraphy, ICS geologic timescale a stage (strat ...
times (in the Late Carboniferous), times in which fossils of ''Adelophthalmus'' have been associated with freshwater
bivalve Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...
s and terrestrial organisms in
coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal i ...
-bearing
strata In geology and related fields, a stratum (: strata) is a layer of Rock (geology), rock or sediment characterized by certain Lithology, lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by v ...
(indicating a
coal swamp Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal i ...
environment). However, this could be related to the diversification of ''Adelophthalmus'' in those epochs more than an ecological change in the whole genus. Most of the ''Adelophthalmus'' species were confined to paralic (in shallow water near the coast) or lowland
basins Basin may refer to: Geography and geology * Depression (geology) ** Back-arc basin, a submarine feature associated with island arcs and subduction zones ** Debris basin, designed to prevent damage from debris flow ** Drainage basin (hydrology), ...
, in
depositional environment In geology, depositional environment or sedimentary environment describes the combination of physical, chemical, and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will b ...
s that had a close connection with marginally marine habitats. For example, during the Moscovian, the Saar-Nahe Basin (where fossils of ''A. granosus'' have been found), was connected or even part of a vast western subsiding area (a sunken zone) in whose drainage went towards the
Paleo-Tethys Ocean The Paleo-Tethys or Palaeo-Tethys Ocean was an ocean located along the northern margin of the paleocontinent Gondwana that started to open during the Middle Cambrian, grew throughout the Paleozoic, and finally closed during the Late Triassic; ex ...
, some 1,500 kilometres (930 miles) towards the south. During the Late
Pennsylvanian Pennsylvanian may refer to: * A person or thing from Pennsylvania * Pennsylvanian (geology) The Pennsylvanian ( , also known as Upper Carboniferous or Late Carboniferous) is, on the International Commission on Stratigraphy, ICS geologic timesc ...
and Early Permian, due to the southern uplift, the drainage began to go north towards the
Panthalassa Ocean Panthalassa, also known as the Panthalassic Ocean or Panthalassan Ocean (from Greek "all" and "sea"), was the vast superocean that encompassed planet Earth and surrounded the supercontinent Pangaea, the latest in a series of supercontinents ...
, increasing the distance to the ocean (about 2,400 km, 1490 mi). ''Adelophthalmus'' is not found in these deposits, while others indicative of a connection with a marginal marine habitat, such as the belinurid
xiphosuran Xiphosura (; , in reference to its sword-like telson) is an order of arthropods related to arachnids. They are more commonly known as horseshoe crabs (a name applied more specifically to the only extant family, Limulidae). They first appeared in t ...
s, persisted. Some of the last occurrences of the adelophthalmids (end of the Carboniferous and Early Permian) seem to have had a kind of reversion in ecological preferences, inhabiting environments with a strong marine influence again, the especially tidally estuarine environments. Adelophthalmidae is considered as a
euryhaline Euryhaline organisms are able to adapt to a wide range of salinities. An example of a euryhaline fish is the short-finned molly, '' Poecilia sphenops'', which can live in fresh water, brackish water, or salt water. The green crab ('' Carcinus m ...
(able to adapt in different salinities) clade that inhabited stressful habitats with regard to paleosalinity and possibly
oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
whose conquest of freshwater habitats was not as successful as in other animals such as the aforementioned bellinurids.


See also

*
List of eurypterid genera This list of eurypterid genera is a comprehensive listing of all genera that have ever been included in the order Eurypterida, excluding purely vernacular terms. The list includes all commonly accepted genera, but also genera that are now consider ...
*
Timeline of eurypterid research This timeline of eurypterid research is a chronologically ordered list of important fossil discoveries, controversies of interpretation, and Biological taxonomy, taxonomic revisions of eurypterids, a group of extinct aquatic arthropods closely re ...


References

{{Taxonbar, from=Q21759233 Adelophthalmoidea Silurian animals Devonian animals Carboniferous animals Permian animals Llandovery first appearances Permian extinctions Prehistoric arthropod families